Significance: South Africa has the highest burden of adolescents living with HIV in the world. Clinical outcomes are poor for adolescents during the transition period. Social media is popular among youth and has potential to improve the modifiable factors in the Social-ecological Model of Adolescent and Young Adult Readiness to Transition (SMART) model such as knowledge, self-efficacy, beliefs, maturity, goals, relationships, peer and social support. The SMART model highlights these modifiable targets of intervention and presents an ideal basis for a behavioral intervention using social media to improve transition care. Innovation: This study will iteratively develop a social media behavioral intervention for adolescents living with HIV and transitioning to adult care in South Africa. This proposal is the first intervention, to our knowledge, designed to address transition outcomes (i.e., retention in care and viral suppression) for HIV-infected adolescents in sub-Saharan Africa where 90% of the pediatric HIV-infections exist. Hypothesis: I hypothesize that an iteratively developed social media based behavioral intervention will be acceptable and feasible for adolescents living with HIV and transitioning to adult care. Approach: I will use in-depth qualitative interviews to determine how social media can overcome barriers and enhance facilitators of successful transition to adult care for adolescents living with HIV in South Africa (Aim 1). I will then iteratively adapt the social media based behavioral intervention, Interactive Transition Support for HIV-infected Adolescents (InTSHA; meaning youth in Zulu), using focus groups with adolescents, their caregivers, and healthcare providers (Aim 2). I will then conduct a pilot clinical trial of the intervention (Aim 3) to determine its acceptability and feasibility. Training Aims: I will undergo didactic study with coursework from the Harvard TH Chan School of Public Health, Harvard Kennedy School, Massachusetts Institute of Technology, and the NIH Office of Social Science and Behavioral Research in: Qualitative research methods for behavioral intervention design, social media use for behavioral interventions, and clinical trials of behavioral interventions. In addition, I will have didactic training with my mentors, attend and present at regular research seminars at Massachusetts General Hospital, conduct formative readings, and participate in the Adolescent Clinical Trials Network (ATN) social media study, iTech. Investigator: Brian Zanoni trained in Internal Medicine/Pediatrics with specialization in Infectious Disease, has extensive clinical experience in adolescent HIV care in South Africa, a strong research foundation, and ample mentorship. Mentors: Jessica Haberer is an expert in global health technology for HIV and serves as Dr. Zanoni?s primary mentor. Christina Psaros is a behavioral scientist and clinical psychologist with expertise in using qualitative research methods for psychosocial aspects of HIV care. Richard Holden is an expert in mobile health technology and behavioral interventions. Kenneth Mayer is an internationally recognized leader in HIV interventions, clinical trials and site principal investigator for the ATN.